These are special reagents used in NMR spectroscopy, in which the majority (>99%) of hydrogen atoms have been replaced by deuterium. Such as: water (D2O), chloroform (CDCl3), dichloromethane (CD2Cl2), dimethyl sulfoxide (DMSO-d6), acetonitrile (CD3CN), methanol (CD3OD), acetone (acetone-d6), benzene (C6D6), toluene (toluene-d8), tetrahydrofuran (THF-d8), and trifluoroacetic acid (TFA-d).